Pilots and astronauts have long been plagued with maintaining operation of their craft while being "blinded" by the sun. It is common practice to provide protective eye gear, in the form of visors, goggles, or sunglasses, which sufficiently filters the sun's light to enable an individual to operate in strong sunlight. Although such devices may satisfactorily filter the sun's rays, they also darken the remaining clear field of view. This presents a dangerous situation for pilots in a combat situation, where the entire field of view must be visually monitored on a constant basis without attenuating light from objects such as approaching hostile aircraft.
In my earlier U.S. Pat. No. 4,848,890, protective eye wear for pilots was disclosed which had the capability of blocking or eclipsing strong light from only that point in the field of vision where sun shines. With the protective gear of my previous patent, a pilot would have a relatively dear field of view where he could sight objects in the sky without being impeded by light filters that otherwise prevent detection of targets and other objects necessary for clear sighting.
My previous invention utilizes a visor with a liquid crystal (LC) matrix over the surface thereof, individual elements of the matrix being selectively energizable to present light blocking points in a wearer's field of vision corresponding to the instantaneous position of the sun in a field of view. As the field of view changes, and more particularly the position of the sun within the field of view, the light blocking LC elements will change within the matrix to correspond with the shifted sun position. A two-dimensional photosensor mounted on the visor detects changing sun position within the field of view so that corresponding LC elements may be activated to a light blocking condition.
The improvement offered by my previous invention not only greatly aids pilots and astronauts but is also applicable to industrial and sports applications where similar problems with light "blindness" may temporarily or permanently impede an individual's sight.
Although my previous invention is quite useful in protecting a wearer from damaging sunlight, it is only useful where a sensing device detects the angle of sunlight falling upon the entire surface of a visor. This would be a problem if a narrow beam of coherent light (e.g. a laser) impinged upon the visor but did not impinge upon the sensor. This is a realistic problem in the battlefield of the future which will undoubtedly be heavily trafficked by laser beams, some as part of range-finding equipment, some to track weapons that are delivering high-speed kinetic-energy projectiles, and some blasting enemy tanks and fortifications with high-energy density laser weapons. The convergence of visible light on the retina increases the energy density by factors of 10.sup.4. Thus, a direct hit of an otherwise harmless laser beam can do permanent damage to a soldier's vision.
At the present time coatings have been developed on glass to reject specific wavelengths that are currently employed in laser operations -- although the appearance of continuously tunable systems makes such filters obsolete. The present technology of coating three-inch-thick glass with a light-sensitive gelatin into which is embedded a diffraction hologram tuned to scatter specific wavelengths has provided the Army with a tank window that will reject laser radiation and defeat kinetic-energy threats of the 30-caliber armor-piercing type. The glass may shatter when struck with a bullet but a polycarbonate backing absorbs the fragments.
Of considerable interest is the planned Army program to develop materials that will reject coherent laser radiation and permit transmittance of nonlethal incoherent radiation. There are a number of concepts on the drawing board.